Blowing my own trumpet here, but look up Radio Control Modeler magazine's plans listings. I've got a design in there called "Squert" which is just what you're after.

Designed when I lived in England and all we could buy were 7.2V motors and 600 AA sized nicads, "Squert" was possibly the first aerobatic S400 model flown there. It really is basic, a box section fuselage, shoulder wing mounted with glue, which is good for hand launches, and a bottom hatch to make changing packs easy. With 8 modern cells and a 6V S400, it should go pretty quick.

Structure is very light, easy to build - if you like woodwork. The plan was published in 1994, but they still crop up. Two showed up at our club's electric funfly last year.